1. Field of the Invention
The present invention relates to a method, a device and the like for counting transmission times of data units having the same variable length.
2. Description of the Related Art
FIG. 9 is a diagram for explaining an example of a process in an RLC sub layer and FIG. 10 is a diagram for explaining a conventional problem with a counter for counting transmission times.
In a radio communication system, user data is transmitted and received between two devices based on a radio communication protocol.
A layer 2 of a protocol for a cellular phone network includes sub layers such as a MAC (Medium Access Control) sub layer, an RLC (Radio Link Control) sub layer and a PDCP (Packet Data Convergence Protocol) sub layer and the like from the lowest.
There are a plurality of PDCP entities and RLC entities corresponding to the number of logical channels (LCH) used by two devices that perform interactive communication.
As shown in FIG. 9, in a device on the transmission side an RLC entity of a certain logical channel divides user data into a plurality of RLC-SDU's (Service Data Units) and generates an RLC-PDU (Protocol Data Unit) by adding a header to each of the RLC-SDU's or by other operation. The header includes protocol control information such as a sequence number.
Furthermore, these RLC-PDU's are processed by the MAC sub layer and the layer 1, and they are sent to the RLC entity of the same logical channel in a device on the reception side.
The RLC-PDU's are sent out from the RLC entity of the device on the transmission side sequentially in the order of the sequence number. Therefore, it is expected that the RLC-PDU's are received sequentially in the order of the sequence number by the RLC entity of the device on the reception side.
If the RLC-PDU that is expected to be received next is not received in the case where a confirmation mode is used, the RLC entity of the device on the reception side regularly requests the RLC entity of the device on the transmission side to retransmit it until it is received. The RLC entity of the device on the transmission side retransmits the RLC-PDU based on the request. In this way, transmission confirmation is performed between both the RLC entities based on the sequence number conventionally.
In addition, as described in “3GPP TS 36.300 V8.1.0 (2007-06)”, published by 3GPP (The 3rd Generation Partnership Project), URL “http://www.3gpp.org/ftp/Specs/archive/36_series/36.300/363 00-810.zip”, searched on the Internet on Aug. 7, 2007, the planning of a new communication standard is carried on. According to this communication standard, the RLC-PDU can have a variable length. Therefore, it becomes possible to divide the RLC-PDU before transmitting and receiving it.
The RLC entity of the device on the transmission side counts the number of times of sending out the RLC-PDU for each RLC-PDU (i.e., for each sequence number). However, if the RLC-PDU is divided into N before sending it out according to the conventional counting method, the number of times of sending out the RLC-PDU becomes N.
More specifically, if the RLC-PDU having the sequence number “0” is transmitted without being divided as shown in FIG. 10 for example (#901), transmission times of the RLC-PDU become “1” (#902). If the RLC-PDU having the sequence number “1” is transmitted without being divided (#903), transmission times of the RLC-PDU become “1” (#904). When the request for retransmission of the RLC-PDU is accepted (#905), the RLC-PDU is retransmitted (#906), and transmission times of the RLC-PDU are increased (incremented) by “1” to be “2” (#907).
If the RLC-PDU having the sequence number “2” is divided into two division units and if a first division unit is transmitted (#908), transmission times of the RLC-PDU become “1” (#909). However, if the other division unit is transmitted (#910), the transmission times of the RLC-PDU are increased by “1” though it is not a retransmission (#911).
In this way, when a data unit such as the RLC-PDU is divided before being transmitted according to the conventional counting method, it is difficult to count correctly substantial transmission times of the data unit.